LoRaWAN Birdhouse

Instead of having an external panel mount puck-style antenna the new birdhouse uses a flexible embedded antenna inside the electronics enclosure (please see the image below). Both antennae are dipoles not requiring a ground plane. The new antenna has the disadvantage of having a solar panel above it which probably affects its radiation pattern.

To compare the performance of the two antennae I gathered some RSSI values using TTN Mapper. In the chart below you can see the average RSSI values for the old (Nr1) and new (Nr2) birdhouse and the LoRaWAN gateways they use. Lower bars (higher RSSI values) in this chart are better. Except for a couple of outliers the new antenna outperformed my expectations. With most gateways the loss is only around 1-2 dB and there are a couple of gateways where the average performance is actually better.

I have replaced the birdhouse today with a new (and hopefully improved) version. The new features include a wall to wall scale on the inside and the electronics, solar cell and antenna are now all in a single enclosure on top of the roof. There are a lot more smaller enhancements which you can check out in the Version2.0.zip file if you are interested (I have moved all of the older design files and images into the Version1.0.zip file).

I just wanted to let you know that shortly after I put the birdhouse back up again another great tit moved into the birdhouse and started building a new nest (please see the image below).

Yesterday morning I took down the birdhouse to investigate the high/drifting weight values (the birds have not returned since last week). There was a lot of mud and moisture underneath the nest built out of moos and down feathers (please see the image below). The moisture caused the veneer on the scale plate to swell and push against the sides. This is what caused the high/drifting weight values (the actual nest by the way only weighs about 80 g). Up until now I have treated the wood only with linseed oil. The oil is environmentally friendly for the birds (it's basically vegetable oil) but apparently doesn't work too well protecting the veneer. I also noticed the gaps between the front panel and the sides of the birdhouse getting bigger. For the next version of the birdhouse I will probably add two more screws to the front/sides of the birdhouse to prevent those gaps from growing. I might even try waterproofing the birdhouse more by using some form of insulation (e.g. foam tape/silicone) between the wood panels. Less moisture on the inside will be good for the veneer (and the birds :-) ).

The weight in the birdhouse reached a maximum two days ago so I got my camera and went to check on the little birds. The dad was sitting in the tree chirping really loud. I think he was trying to get the young ones to leave the nest. And the mom was still bringing in food and carrying out waste. I'm kind of puzzled by the 300 gram maximum weight. An adult bird weighs between 15 and 20 g. If I subtract about 50 g for the nest there is about 250 g that need to be accounted for. Even if a fledgling weighs about 15 g that makes for a lot of birds (maybe there are feces left in the birdhouse adding to the weight).

Around April 26th the weight in the birdhouse started going up again. To me this looks like the eggs have hatched and there are now chicks inside the birdhouse which are growing in size and weight. Next up, if I'm not mistaken, should be a drop in weight in about two weeks time when the fledglings leave the nest. It amazes me to see how fast all of this is happening :-) .

After gathering more than 40 grams of nesting material there seems to be a change happening inside the birdhouse. Before April 13th you can see the little bird coming into the birdhouse at night to sleep. After April 13th it looks like there is now someone permanently inside the birdhouse. I'm guessing this is probably the female nesting.

The weather has been nice and dry for the last few days and the little bird has started bringing in nesting material. There is about 20 grams of material in the birdhouse right now (that is more than the weight of the bird itself).

Ever since about mid February the birdhouse has started seeing visits during the daytime. I'm guessing that the little bird is bringing in material to build a nest/defend it's territory. There are some good infos about the breeding habits of the great tit on Wikipedia in case you are interested.

I have been testing the new scale in recent days. One thing that surprised me was the temperature coefficient of the new load cell. To determine the temperature coefficient I had put the scale into the freezer of my refrigerator and watched it warm up just like with the previous scale. I had expected to get a negative temperature coefficient just like with the first one (please see the older posts). But this one has a slightly positive temperature coefficient even though it is the same brand and type of load cell. It looks like each of these load cells need to be tested and measured before being put to use.

I use the following formula to correct the positive temperature coefficient:

And this is what the graph looks like with the correction applied:

There are some good videos on YouTube about the errors (zero, span, linearity) in pressure sensors in case you're interested.